For example, a toilet seat is configured by bonding a bottom plate provided on the toilet side to a top plate contacted by the buttocks. Patent Literature 1 describes technology in which these parts made of resin are bonded by filling a bonding resin into a passageway formed between the parts made of resin.
When a user of the toilet sits on the toilet seat, a load is applied to the toilet seat; and stress due to compression and stress due to tension are generated at the vicinity of the bonding part between the top plate and the bottom plate. The bonding member that bonds the top plate and the bottom plate is weaker than the top plate and the bottom plate. In particular, when an excessive stress is applied to an exposed surface of the bonding member exposed externally, peeling may occur and a gap may occur between the top plate and the bonding member or between the bottom plate and the bonding member. When the gap occurs in the toilet seat, dirt collects in the gap. The dirt that collects in the gap is not easy to remove when cleaning. Accordingly, when the gap occurs in the toilet seat, the cleanability of the toilet seat undesirably degrades.